The MTR Corporation is today facing mounting pressure from lawmakers to come clean on how much it knew about the huge rock formation which delayed the completion of the cross-border high-speed railway project.

Michael Tien Puk-sun, who chairs the Legislative Council’s rail subcommittee, said today that the timing of precisely when the MTR became aware of the granite formation was crucial and could point to a “cover up”.

The latest questions arose after the Chinese-language Apple Daily today published two consultancy documents dated 2009 and 2010, suggesting the MTR could have known about the problem in as early as four years ago.

The newspaper said the documents – including a report on geological conditions and a map showing positions of drilling tests – showed hard granite rocks were found between 15 and 30 metres below the ground level on some locations.

If accurate, the documents contradict an explanation given by MTR chiefs on Monday on the HK$67 billion project’s two-year delay – from 2015 to 2017 – that the granite was “unpredictable”. The rail link, which will connect Hong Kong and Guangzhou, is costing HK$2.6 billion for each of its 26 kilometres.

“It does not necessarily amount to a cover-up if MTR has known about the granite’s existence in 2010. But the question is if [the management] knew about its complexity and impact to the construction.” the New People’s Party lawmaker said today.

“It could have been a cover-up or mismanagement. The timing is crucial,” said Tien. “They have to come clean on the issue on the subcommittee meeting on May 5.”

Federation of Trade Union lawmaker Wong Kwok-hing said there were a lot of unanswered questions that MTR and the government have to explain. “But we have to wait for their answers on the subcommittee meeting on May 5,” said Wong.

The MTR board has set up an “independent” committee of non-executive directors to review management of the delayed cross-border express railway and find out why it was not briefed earlier on the problems.

But pro-establishment lawmaker Frankie Yick Chi-ming said the committee should include independent consultants and third-party professionals.

“It raises doubts if it is only the non-executive directors [of the MTR] who are leading the investigation since it gives the public an impression that it is their own people probing themselves,” Yick said.

At next Monday’s Legco meeting, Yick said the MTR should at least explain why it failed to identify earlier how big an obstacle the geological conditions at the terminus site pose and whether there had been any groundwork investigation conducted at the area where a golf driving range used to sit.

Lawmakers who visited the high-speed railway West Kowloon terminus on Monday were told that there had probably been no survey ever conducted at the area for the project since the MTR was not granted access.

On whether he supports a move to invoke the Legco’s special investigative powers to force the MTR to submit all relevant documents, he said he would wait until he hears MTR’s explanation and added that it would be more appropriate to leave any such investigation to professionals.